U.S. patent application number 17/562440 was filed with the patent office on 2022-09-22 for polymer electrolyte membrane, method for preparing the membrane and fuel cell comprising the membrane.
This patent application is currently assigned to HYUNDAI MOBIS CO., LTD.. The applicant listed for this patent is Dankook University Cheonan Campus Industry Academic Cooperation Foundation, HYUNDAI MOBIS CO., LTD.. Invention is credited to Seung Kyu CHOI, Pil Won HEO, Ki Young JEONG, Eun Heui KANG, Chang Hyun LEE, Sung Chul LEE, In Kee PARK.
Application Number | 20220302488 17/562440 |
Document ID | / |
Family ID | 1000006138929 |
Filed Date | 2022-09-22 |
United States Patent
Application |
20220302488 |
Kind Code |
A1 |
HEO; Pil Won ; et
al. |
September 22, 2022 |
POLYMER ELECTROLYTE MEMBRANE, METHOD FOR PREPARING THE MEMBRANE AND
FUEL CELL COMPRISING THE MEMBRANE
Abstract
The polymer electrolyte membrane includes: a first ion
conductive polymer layer; and a second ion conductive polymer layer
disposed on at least one surface of the first ion conductive
polymer layer, wherein the first ion conductive polymer layer
comprises a first ion conductive polymer comprising a sulfonic acid
group, wherein the second ion conductive polymer layer comprises a
second ion conductive polymer comprising a carboxylic acid group,
and wherein a thickness of the second ion conductive polymer layer
is in a range of 1% to 80% of a thickness of the polymer
electrolyte membrane. Further, disclosed are the method for
preparing the same, the membrane-electrode assembly including the
same, and the fuel cell including the same.
Inventors: |
HEO; Pil Won; (Hwaseong-si,
KR) ; LEE; Sung Chul; (Yongin-si, KR) ; KANG;
Eun Heui; (Suwon-si, KR) ; CHOI; Seung Kyu;
(Suwon-si, KR) ; JEONG; Ki Young; (Suwon-si,
KR) ; LEE; Chang Hyun; (Seongnam-si, KR) ;
PARK; In Kee; (Cheonan-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HYUNDAI MOBIS CO., LTD.
Dankook University Cheonan Campus Industry Academic Cooperation
Foundation |
Seoul
Cheonan-si |
|
KR
KR |
|
|
Assignee: |
HYUNDAI MOBIS CO., LTD.
Seoul
KR
Dankook University Cheonan Campus Industry Academic Cooperation
Foundation
Cheonan-si
KR
|
Family ID: |
1000006138929 |
Appl. No.: |
17/562440 |
Filed: |
December 27, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 8/1053 20130101;
H01M 8/1039 20130101; H01M 8/1072 20130101; H01M 8/109
20130101 |
International
Class: |
H01M 8/1053 20060101
H01M008/1053; H01M 8/1039 20060101 H01M008/1039; H01M 8/1072
20060101 H01M008/1072; H01M 8/1086 20060101 H01M008/1086 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 16, 2021 |
KR |
10-2021-0034254 |
Claims
1. A polymer electrolyte membrane comprising: a first ion
conductive polymer layer; and a second ion conductive polymer layer
disposed on at least one surface of the first ion conductive
polymer layer, wherein the first ion conductive polymer layer
comprises a first ion conductive polymer comprising a sulfonic acid
group, wherein the second ion conductive polymer layer comprises a
second ion conductive polymer comprising a carboxylic acid group,
and wherein a thickness of the second ion conductive polymer layer
is in a range of 1% to 80% of a thickness of the polymer
electrolyte membrane.
2. The polymer electrolyte membrane of claim 1, wherein the second
ion conductive polymer layer comprises: a third ion conductive
polymer layer disposed on at least one surface of the first ion
conductive polymer layer; and a fourth ion conductive polymer layer
disposed on one surface of the third ion conductive polymer layer,
wherein the third ion conductive polymer layer comprises a third
ion conductive polymer comprising the carboxylic acid group and the
sulfonic acid group, and wherein the fourth ion conductive polymer
layer comprises a fourth ion conductive polymer comprising the
carboxylic acid group.
3. The polymer electrolyte membrane of claim 2, wherein a thickness
of the third ion conductive polymer layer is in a range of 1 to 40%
of the thickness of the polymer electrolyte membrane, and wherein a
thickness of the fourth ion conductive polymer layer is in a range
of 1 to 40% of the thickness of the polymer electrolyte
membrane.
4. The polymer electrolyte membrane of claim 2, wherein the third
ion conductive polymer layer has a first concentration gradient of
the carboxylic acid group and a second concentration gradient of
the sulfonic acid group.
5. The polymer electrolyte membrane of claim 4, wherein the first
concentration gradient of the carboxylic acid group increases in a
thickness direction from the first ion conductive polymer layer to
the fourth ion conductive polymer layer, and the second
concentration gradient of the sulfonic acid group decreases in the
thickness direction from the first ion conductive polymer layer to
the fourth ion conductive polymer layer.
6. The polymer electrolyte membrane of claim 1, wherein the polymer
electrolyte membrane comprises: the first ion conductive polymer
layer; and the second ion conductive polymer layer disposed one
surface of the first ion conductive polymer layer, wherein the
thickness of the second ion conductive polymer layer is in a range
of 1 to 40% of the thickness of the polymer electrolyte
membrane.
7. The polymer electrolyte membrane of claim 1, wherein the polymer
electrolyte membrane comprises: the first ion conductive polymer
layer; and a plurality of the second ion conductive polymer layers
respectively disposed on both opposing surfaces of the first ion
conductive polymer layer, wherein a thickness of each of the
plurality of the second ion conductive polymer layers is in a range
of 1 to 40% of the thickness of the polymer electrolyte
membrane.
8. The polymer electrolyte membrane of claim 1, wherein the
thickness of the polymer electrolyte membrane is in a range of 10
.mu.m to 100 .mu.m.
9. The polymer electrolyte membrane of claim 1, wherein the first
ion conductive polymer comprises a sulfonated product of at least
one polymer selected from the group consisting of a fluoropolymer,
a hydrocarbon-based polymer, and a partially fluorinated
polymer.
10. The polymer electrolyte membrane of claim 1, wherein the first
ion conductive polymer layer comprises a porous substrate.
11. The polymer electrolyte membrane of claim 1, wherein the
polymer electrolyte membrane has a hydrogen permeability of 18.5
Barrer or less at 70.degree. C. as measured using a time-lag
method.
12. The polymer electrolyte membrane of claim 1, wherein the
polymer electrolyte membrane has an oxygen permeability of less
than 4.0 Barrer at 70.degree. C. as measured using a time-lag
method.
13. A method for preparing a polymer electrolyte membrane
comprising: preparing a first ion conductive polymer membrane
comprising a first ion conductive polymer layer comprising a
sulfonic acid group; performing a chlorination reaction on at least
one surface of the first ion conductive polymer membrane for 5 to
30 minutes such that a second ion conductive polymer membrane
comprising a chlorinated ion conductive polymer layer is formed on
at least one surface of the first ion conductive polymer layer,
wherein the chlorinated ion conductive polymer layer is formed by
partially chlorinating the sulfonic acid group; performing a
nitrilation reaction on the second ion conductive polymer membrane
such that a third ion conductive polymer membrane comprising a
nitrilated ion conductive polymer layer is formed on at least one
surface of the first ion conductive polymer layer, wherein the
nitrilated ion conductive polymer layer is formed by replacing a
chlorine in the chlorinated ion conductive polymer layer with a
nitrile group; performing a hydrolysis reaction on the third ion
conductive polymer membrane such that a fourth ion conductive
polymer membrane comprising a second ion conductive polymer layer
is formed on at least one surface of the first ion conductive
polymer layer, wherein the second ion conductive polymer layer is
formed by replacing the nitrile group of the nitrilated ion
conductive polymer layer with a carboxylic acid group; and
performing heat treatment on the fourth ion conductive polymer
membrane at .+-.10.degree. C. around a glass transition temperature
of an ion conductive polymer comprising a carboxylic acid group,
thereby preparing the polymer electrolyte membrane, wherein a
thickness of the second ion conductive polymer layer is in a range
of 1 to 80% of a thickness of the polymer electrolyte membrane.
14. The method of claim 13, wherein the performing the chlorination
reaction comprises immersing the first ion conductive polymer
membrane in a chlorination reaction solution comprising a
hydrochloric acid and an ammonium chloride.
15. A membrane-electrode assembly comprising a negative-electrode;
a positive-electrode; and a polymer electrolyte membrane comprising
the polymer electrolyte membrane of claim 1, interposed between the
negative-electrode and the positive-electrode.
16. A fuel cell comprising the membrane-electrode assembly of claim
15.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of priority to Korean
Patent Application No. 10-2021-0034254, filed in the Korean
Intellectual Property Office on Mar. 16, 2021, the entire contents
of which are incorporated herein by reference.
BACKGROUND
1. Field
[0002] The following description relates to a polymer electrolyte
membrane, and more particularly, to a polymer electrolyte membrane
for a fuel cell with excellent reaction gas barrier ability, a
method for preparing the same, a membrane-electrode assembly
including the same, and a fuel cell including the same.
2. Discussion of Related Art
[0003] A fuel cell electrochemically oxidizes fuels such as
hydrogen and methanol in the cell to convert chemical energy of the
fuels into electrical energy. In particular, a polymer electrolyte
membrane fuel cell (PEFC) uses a solid polymer electrolyte membrane
with ion conductive properties, and thus operates at a
low-temperature, compared to a high-temperature operating fuel cell
such as a solid oxide fuel cell (SOFC), and achieves a simple
system, and thus is used as a power source for vehicles and
buildings.
[0004] Main characteristics required for a solid polymer
electrolyte membrane of the polymer electrolyte membrane fuel cell
include mechanical properties for physical durability, high
hydrogen ion conductivity for realization of performance, and
reaction gas barrier ability to improve fuel cell efficiency and
chemical durability.
[0005] In this connection, when there is a defect in the solid
polymer electrolyte membrane or when micropores exist therein,
there may be a trace amount of reaction gas permeation. Thus, the
permeation of gas such as hydrogen and air produce chemical
radicals (e.g., hydroxyl radicals) to promote structural
decomposition of the solid polymer electrolyte by the radicals.
This may result in thinning of the solid polymer electrolyte
membrane during operation of the fuel cell. Thus, a pinhole may
occur and spread, which is a direct cause of shortening a lifespan
of a membrane-electrode assembly of the fuel cell.
SUMMARY
[0006] This Summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This Summary is not intended to identify
key features or essential features of the claimed subject matter,
nor is it intended to be used as an aid in determining the scope of
the claimed subject matter.
[0007] In one general aspect, there is provided a polymer
electrolyte membrane including: a first ion conductive polymer
layer; and a second ion conductive polymer layer disposed on at
least one surface of the first ion conductive polymer layer,
wherein the first ion conductive polymer layer includes a first ion
conductive polymer including a sulfonic acid group, wherein the
second ion conductive polymer layer includes a second ion
conductive polymer comprising a carboxylic acid group, and wherein
a thickness of the second ion conductive polymer layer is in a
range of 1% to 80% of a thickness of the polymer electrolyte
membrane.
[0008] The second ion conductive polymer layer may include: a third
ion conductive polymer layer disposed on at least one surface of
the first ion conductive polymer layer; and a fourth ion conductive
polymer layer disposed on one surface of the third ion conductive
polymer layer, wherein the third ion conductive polymer layer may
include a third ion conductive polymer including the carboxylic
acid group and the sulfonic acid group, and wherein the fourth ion
conductive polymer layer may include a fourth ion conductive
polymer including the carboxylic acid group.
[0009] A thickness of the third ion conductive polymer layer may be
in a range of 1 to 40% of the thickness of the polymer electrolyte
membrane, and wherein a thickness of the fourth ion conductive
polymer layer may be in a range of 1 to 40% of the thickness of the
polymer electrolyte membrane.
[0010] The third ion conductive polymer layer may have a first
concentration gradient of the carboxylic acid group and a second
concentration gradient of the sulfonic acid group.
[0011] The first concentration gradient of the carboxylic acid
group may increase in a thickness direction from the first ion
conductive polymer layer to the fourth ion conductive polymer
layer, and the second concentration gradient of the sulfonic acid
group may decrease in the thickness direction from the first ion
conductive polymer layer to the fourth ion conductive polymer
layer.
[0012] The polymer electrolyte membrane may include: the first ion
conductive polymer layer; and the second ion conductive polymer
layer disposed one surface of the first ion conductive polymer
layer, wherein the thickness of the second ion conductive polymer
layer may be a range of 1 to 40% of the thickness of the polymer
electrolyte membrane.
[0013] The polymer electrolyte membrane may include: the first ion
conductive polymer layer; and a plurality of the second ion
conductive polymer layers respectively disposed on both opposing
surfaces of the first ion conductive polymer layer, wherein a
thickness of each of the plurality of the second ion conductive
polymer layers may be in a range of 1 to 40% of the thickness of
the polymer electrolyte membrane.
[0014] The thickness of the polymer electrolyte membrane may be in
a range of 10 .mu.m to 100 .mu.m.
[0015] The first ion conductive polymer may include a sulfonated
product of at least one polymer selected from the group consisting
of a fluoropolymer, a hydrocarbon-based polymer, and a partially
fluorinated polymer.
[0016] The first ion conductive polymer layer may include a porous
substrate.
[0017] The polymer electrolyte membrane may have a hydrogen
permeability of 18.5 Barrer or less at 70.degree. C. as measured
using a time-lag method.
[0018] The polymer electrolyte membrane may have an oxygen
permeability of less than 4.0 Barrer at 70.degree. C. as measured
using a time-lag method.
[0019] In another general aspect, there is provided a method for
preparing a polymer electrolyte membrane including: preparing a
first ion conductive polymer membrane including a first ion
conductive polymer layer including a sulfonic acid group;
performing a chlorination reaction on at least one surface of the
first ion conductive polymer membrane for 5 to 30 minutes such that
a second ion conductive polymer membrane including a chlorinated
ion conductive polymer layer is formed on at least one surface of
the first ion conductive polymer layer, wherein the chlorinated ion
conductive polymer layer is formed by partially chlorinating the
sulfonic acid group; performing a nitrilation reaction on the
second ion conductive polymer membrane such that a third ion
conductive polymer membrane including a nitrilated ion conductive
polymer layer is formed on at least one surface of the first ion
conductive polymer layer, wherein the nitrilated ion conductive
polymer layer is formed by replacing a chlorine in the chlorinated
ion conductive polymer layer with a nitrile group; performing a
hydrolysis reaction on the third ion conductive polymer membrane
such that a fourth ion conductive polymer membrane including a
second ion conductive polymer layer is formed on at least one
surface of the first ion conductive polymer layer, wherein the
second ion conductive polymer layer is formed by replacing the
nitrile group of the nitrilated ion conductive polymer layer with a
carboxylic acid group; and performing heat treatment on the fourth
ion conductive polymer membrane at .+-.10.degree. C. around a glass
transition temperature of an ion conductive polymer including a
carboxylic acid group, thereby preparing the polymer electrolyte
membrane, wherein a thickness of the second ion conductive polymer
layer is in a range of 1 to 80% of a thickness of the polymer
electrolyte membrane.
[0020] The performing the chlorination reaction may include
immersing the first ion conductive polymer membrane in a
chlorination reaction solution including a hydrochloric acid and an
ammonium chloride.
[0021] In still another general aspect, there is provided a
membrane-electrode assembly including a negative-electrode; a
positive-electrode; and a polymer electrolyte membrane including
the polymer electrolyte membrane, interposed between the
negative-electrode and the positive-electrode.
[0022] In still another general aspect, there is provided a fuel
cell including the membrane-electrode assembly.
[0023] Other features and aspects will be apparent from the
following detailed description, the drawings, and the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a graph showing results of dynamic mechanical
analysis based on a type of an ion conductive group (sulfonic acid
group and carboxylic acid group) contained in an ion conductive
polymer of a polymer electrolyte membrane used in example of the
present disclosure.
[0025] FIG. 2 shows a photograph taken and analyzed via a line scan
method using SEM-EDX (Scanning Electron Microscope-Energy
Dispersive X-ray Spectrometer), about a cross section of a polymer
electrolyte membrane after hydrogen ions of a polymer electrolyte
membrane prepared in Example 2 of the present disclosure are
replaced with sodium ions.
[0026] FIG. 3 is a graph showing hydrogen permeability based on a
temperature as measured using a time-lag method, about a polymer
electrolyte membrane prepared in each of Examples 1 and 2 and
Comparative Examples 1 and 2 of the present disclosure.
[0027] FIG. 4 is a graph showing oxygen permeability based on a
temperature as measured using a time-lag method, about a polymer
electrolyte membrane prepared in each of Examples 1 and 2 and
Comparative Examples 1 and 2 of the present disclosure.
[0028] Throughout the drawings and the detailed description, unless
otherwise described or provided, the same drawing reference
numerals will be understood to refer to the same elements,
features, and structures. The drawings may not be to scale, and the
relative size, proportions, and depiction of elements in the
drawings may be exaggerated for clarity, illustration, and
convenience.
DETAILED DESCRIPTION
[0029] The following detailed description is provided to assist the
reader in gaining a comprehensive understanding of the methods,
apparatuses, and/or systems described herein. However, various
changes, modifications, and equivalents of the methods,
apparatuses, and/or systems described herein will be apparent after
an understanding of the disclosure of this application. For
example, the sequences of operations described herein are merely
examples, and are not limited to those set forth herein, but may be
changed as will be apparent after an understanding of the
disclosure of this application, with the exception of operations
necessarily occurring in a certain order. Also, descriptions of
features that are known may be omitted for increased clarity and
conciseness.
[0030] The features described herein may be embodied in different
forms, and are not to be construed as being limited to the examples
described herein. Rather, the examples described herein have been
provided merely to illustrate some of the many possible ways of
implementing the methods, apparatuses, and/or systems described
herein that will be apparent after an understanding of the
disclosure of this application.
[0031] The terminology used herein is for the purpose of describing
particular examples only and is not to be limiting of the examples.
The singular forms "a", "an", and "the" are intended to include the
plural forms as well, unless the context clearly indicates
otherwise. It will be further understood that the terms
"comprises/comprising" and/or "includes/including" when used
herein, specify the presence of stated features, integers, steps,
operations, elements, and/or components, but do not preclude the
presence or addition of one or more other features, integers,
steps, operations, elements, components and/or groups thereof.
[0032] When one constituent element is described as being
"connected", "coupled", or "attached" to another constituent
element, it should be understood that one constituent element can
be connected or attached directly to another constituent element,
and an intervening constituent element can also be "connected",
"coupled", or "attached" to the constituent elements.
[0033] The terms or words used in the present specification and
claims should not be construed as being limited to conventional or
dictionary meanings. Rather, based on a principle that the inventor
may adequately define concepts of the terms to describe his/her
invention in the best way, the terms should be interpreted as a
meaning and concept consistent with the technical idea of the
present disclosure.
[0034] In the present disclosure, a term `polymer` is meant to
include both a homopolymer in which one type of monomer is
polymerized and a copolymer in which two or more types of
comonomers are copolymerized.
[0035] In the present disclosure, a term `ion conductive polymer`
is meant to include both a polymer containing an ion conductive
group on a main chain of the polymer, as well as an intermediate of
a reaction for imparting the ion conductive group to the main chain
of the polymer. Therefore, when each of a chlorinated ion
conductive polymer of a chlorinated ion conductive polymer layer,
and a nitrilated ion conductive polymer of a nitrilated ion
conductive polymer layer as described in a preparation method of
the polymer electrolyte membrane described in the present
disclosure is free of the ion conductive group, each of the
chlorinated ion conductive polymer and the nitrilated ion
conductive polymer acts as an intermediate of the reaction to
prepare the ion conductive polymer and thus belongs to the ion
conductive polymer.
[0036] It will be understood that, although the terms "first",
"second", "third", and so on may be used herein to describe various
elements, components, regions, layers and/or sections, these
elements, components, regions, layers and/or sections should not be
limited by these terms. These terms are used to distinguish one
element, component, region, layer or section from another element,
component, region, layer or section. Thus, a first element,
component, region, layer or section described below could be termed
a second element, component, region, layer or section, without
departing from the spirit and scope of the present disclosure.
[0037] The present disclosure provides a polymer electrolyte
membrane. The polymer electrolyte membrane may be a polymer
electrolyte membrane for a fuel cell. In a specific example, the
polymer electrolyte membrane for a polymer electrolyte membrane
fuel cell (PEFC).
[0038] According to one embodiment of the present disclosure, the
polymer electrolyte membrane includes a first ion conductive
polymer layer; and a second ion conductive polymer layer formed in
at least one surface of the first ion conductive polymer layer,
wherein the first ion conductive polymer layer includes an ion
conductive polymer containing a sulfonic acid group, wherein the
second ion conductive polymer layer includes an ion conductive
polymer containing a carboxylic acid group, wherein a thickness of
the second ion conductive polymer layer may be in a range of 1% to
80% of a thickness of the polymer electrolyte membrane.
[0039] According to one embodiment of the present disclosure, the
polymer electrolyte membrane includes the second ion conductive
polymer layer. Thus, a sp2 hybrid structure from the carboxylic
acid group and a dimer due to a hydrogen bond may be achieved,
thereby achieving a cross-linked structure. In addition, when the
polymer electrolyte membrane is applied on an ionomer electrode and
is used as a membrane surface layer of a membrane-electrode
assembly, the polymer electrolyte membrane may exhibit high
mechanical properties in humid and low humidity conditions. In
addition, chemical stability may be ensured, and thus, reaction gas
barrier ability of the polymer electrolyte membrane may be
improved. However, the carboxylic acid group has lower ionic
conductivity than that of the sulfonic acid group. Thus, when all
sulfonic acid groups of the polymer electrolyte membrane are
substituted or modified into the carboxylic acid groups, the
polymer electrolyte membrane itself may lose a hydrogen ion
conduction function, apart from the improvement of the mechanical
properties and chemical stability as described above. Therefore, it
is very important to control the thickness of the second ion
conductive polymer layer in order to that the polymer electrolyte
membrane according to the present disclosure simultaneously secures
the mechanical properties and chemical stability while basically
maintaining the ion conductivity of the polymer electrolyte
membrane. In this regard, the thickness of the second ion
conductive polymer layer may be 1% or more, 5% or more, 10% or
more, 15% or more, or 20% or more of the thickness of the polymer
electrolyte membrane, and may be 80% or less, 60% or less, 50% or
less, 45% or less, or 40% or less of the thickness of the polymer
electrolyte membrane.
[0040] According to one embodiment of the present disclosure, the
polymer electrolyte membrane may be prepared by a preparation
method of the polymer electrolyte membrane to be described below.
In a specific example, the second ion conductive polymer layer may
be formed by modifying at least one surface of the first ion
conductive polymer layer. Accordingly, the second ion conductive
polymer layer includes a third ion conductive polymer layer
including an ion conductive polymer in which some of the sulfonic
acid groups in at least one surface of the first ion conductive
polymer layer are modified into carboxylic acid groups; and a
fourth ion conductive polymer layer including an ion conductive
polymer in which all of the sulfonic acid groups in at least one
surface of the first ion conductive polymer layer are modified into
carboxylic acid groups.
[0041] In other words, the second ion conductive polymer layer may
include: the third ion conductive polymer layer formed in at least
one surface of the first ion conductive polymer layer; and the
fourth ion conductive polymer layer formed in one surface of the
third ion conductive polymer layer, wherein the third ion
conductive polymer layer includes an ion conductive polymer
containing a carboxylic acid group and a sulfonic acid group,
wherein the fourth ion conductive polymer layer includes an ion
conductive polymer containing a carboxylic acid group.
[0042] That is, the polymer electrolyte membrane according to one
embodiment of the present disclosure may include the first ion
conductive polymer layer; the third ion conductive polymer layer
formed in at least one surface of the first ion conductive polymer
layer; and the fourth ion conductive polymer layer formed in one
surface of the third ion conductive polymer layer.
[0043] According to one embodiment of the present disclosure, for
the same reason for which the thickness of the second ion
conductive polymer layer is adjusted as described above, a
thickness of the third ion conductive polymer layer may be in a
range of 1% to 40% of the thickness of the polymer electrolyte
membrane. When this defined range is met, the mechanical properties
and chemical stability may be secured at the same time while
basically maintaining the ion conductivity of the polymer
electrolyte membrane, and the reaction gas barrier ability of the
polymer electrolyte membrane may be particularly excellent. In a
specific example, the thickness of the third ion conductive polymer
layer may be 1% or more, 2.5% or more, 5% or more, 7.5% or more, or
10% or more of the thickness of the polymer electrolyte membrane,
and may be 40% or less, 30% or less, 25% or less, or 20% or less of
the thickness of the polymer electrolyte membrane.
[0044] According to one embodiment of the present disclosure, for
the same reason for which the thickness of the second ion
conductive polymer layer is adjusted as described above, the
thickness of the fourth ion conductive polymer layer may be in a
range of 1% to 40% of the thickness of the polymer electrolyte
membrane. When this defined range is met, the mechanical properties
and chemical stability may be secured at the same time while
basically maintaining the ion conductivity of the polymer
electrolyte membrane, and the reaction gas barrier ability of the
polymer electrolyte membrane may be particularly excellent. In a
specific example, the thickness of the fourth ion conductive
polymer layer may be 1% or more, 2.5% or more, 5% or more, 7.5% or
more, or 10% or more of the thickness of the polymer electrolyte
membrane, and may be 40% or less, 30% or less, 25% or less, or 20%
or less of the thickness of the polymer electrolyte membrane.
[0045] According to one embodiment of the present disclosure, the
third ion conductive polymer layer may have a concentration
gradient of each of the carboxylic acid group and the sulfonic acid
group of the ion conductive polymer containing a carboxylic acid
group and a sulfonic acid group. In this connection, the
concentration gradient is not limited to a case in which the
concentration itself has a gradient according to the dictionary
definition, but means that a molar ratio or a weight ratio of the
carboxylic acid group and the sulfonic acid group has a
gradient.
[0046] According to one embodiment of the present disclosure, the
third ion conductive polymer layer includes the ion conductive
polymer containing both of the carboxylic acid group and the
sulfonic acid group. In this connection, each of the carboxylic
acid group and the sulfonic acid group may not be distributed at a
constant or uniform concentration across the ion conductive polymer
included in the third ion conductive polymer layer, but may be
distributed so as to have a concentration gradient across the ion
conductive polymer. This may be achieved by preparing the polymer
electrolyte membrane according to the present disclosure using the
preparation method of the polymer electrolyte membrane as described
subsequently. When the polymer electrolyte membrane includes the
third ion conductive polymer layer including the ion conductive
polymer in which each of the carboxylic acid group and the sulfonic
acid group of the ion conductive polymer has the concentration
gradient, the reaction gas barrier ability may be further improved
while preventing the deterioration of the ion conductivity of the
electrolyte membrane, compared to a case where the first ion
conductive polymer layer including the ion conductive polymer
containing the sulfonic acid group and the fourth ion conductive
polymer layer including the ion conductive polymer containing the
carboxylic acid group are in direct contact with each other.
[0047] According to one embodiment of the present disclosure, the
third ion conductive polymer layer may be composed such that the
carboxylic acid group of the ion conductive polymer containing both
of the carboxylic acid group and the sulfonic acid group has a
gradient in which a concentration of the carboxylic acid group
increases in a thickness direction from the first ion conductive
polymer layer to the fourth ion conductive polymer layer, and the
sulfonic acid group of the ion conductive polymer containing both
of the carboxylic acid group and the sulfonic acid group has a
concentration gradient in which a concentration of the sulfonic
acid group decreases in the thickness direction from the first ion
conductive polymer layer to the fourth ion conductive polymer
layer.
[0048] According to one embodiment of the present disclosure, the
polymer electrolyte membrane may include a first ion conductive
polymer layer; and a second ion conductive polymer layer formed in
one surface of the first ion conductive polymer layer, wherein a
thickness of the second ion conductive polymer layer may be in a
range of 1% to 40% of a thickness of the polymer electrolyte
membrane. That is, the polymer electrolyte membrane may include a
stack structure including `the first ion conductive polymer
layer/the second ion conductive polymer layer`.
[0049] According to one embodiment of the present disclosure, when
the polymer electrolyte membrane includes the second ion conductive
polymer layer formed in one surface of the first ion conductive
polymer layer, the thickness of the second ion conductive polymer
layer may be 1% or more, 2.5% or more, 5% or more, 7.5% or more, or
10% or more of the thickness of the polymer electrolyte membrane,
and may be 40% or less, 30% or less, 25% or less, or 20% or less of
the thickness of the polymer electrolyte membrane. When this
defined range is met, the mechanical properties and chemical
stability may be secured at the same time while basically
maintaining the ion conductivity of the polymer electrolyte
membrane, and the reaction gas barrier ability of the polymer
electrolyte membrane may be particularly excellent.
[0050] According to one embodiment of the present disclosure, the
polymer electrolyte membrane may include a first ion conductive
polymer layer; a third ion conductive polymer layer formed in one
surface of the first ion conductive polymer layer; and a fourth ion
conductive polymer layer formed in one surface of the third ion
conductive polymer layer. That is, the polymer electrolyte membrane
may include a stack structure including `the first ion conductive
polymer layer/the third ion conductive polymer layer/the fourth ion
conductive polymer layer`. In this connection, a thickness of the
third ion conductive polymer layer may be in a range of 0.5% to 20%
of the thickness of the polymer electrolyte membrane, and a
thickness of the fourth ion conductive polymer layer may be in a
range of 0.5% to 20% of the thickness of the polymer electrolyte
membrane. When this defined range is met, the mechanical properties
and chemical stability may be secured at the same time while
basically maintaining the ion conductivity of the polymer
electrolyte membrane, and the reaction gas barrier ability of the
polymer electrolyte membrane may be particularly excellent. In this
connection, in a specific example, each of the thickness of the
third ion conductive polymer layer and the thickness of the fourth
ion conductive polymer layer may be 0.5% or more, 1.25% or more,
2.5% or more, 3.75% or more, or 5% or more of the thickness of the
polymer electrolyte membrane, and may be 20% or less, 15% or less,
12.5% or less, or 10% or less of the thickness of the polymer
electrolyte membrane.
[0051] According to one embodiment of the present disclosure, the
polymer electrolyte membrane may include a first ion conductive
polymer layer; and a plurality of second ion conductive polymer
layers respectively formed in both opposing surfaces of the first
ion conductive polymer layer, wherein a thickness of each of the
plurality of second ion conductive polymer layers may be in a range
of 1% to 40% of the thickness of the polymer electrolyte membrane.
That is, the polymer electrolyte membrane may include a stack
structure including `the second ion conductive polymer layer/the
first ion conductive polymer layer/the second ion conductive
polymer layer`.
[0052] According to one embodiment of the present disclosure, when
the polymer electrolyte membrane includes the plurality of second
ion conductive polymer layers respectively formed in both opposing
surfaces of the first ion conductive polymer layer, the thickness
of each of the plurality of second ion conductive polymer layers
may be in a range of 1% to 40% of the thickness of the polymer
electrolyte membrane. When this defined range is met, the
mechanical properties and chemical stability may be secured at the
same time while basically maintaining the ion conductivity of the
polymer electrolyte membrane, and the reaction gas barrier ability
of the polymer electrolyte membrane may be particularly excellent.
In this connection, in a specific example, the thickness of each of
the plurality of second ion conductive polymer layers may be 1% or
more, 2.5% or more, 5% or more, 7.5% or more, or 10% or more of the
thickness of the polymer electrolyte membrane, and may be 40% or
less, 30% or less, 25% or less, or 20% or less of the thickness of
the polymer electrolyte membrane.
[0053] According to one embodiment of the present disclosure, the
polymer electrolyte membrane may include a first ion conductive
polymer layer; a plurality of third ion conductive polymer layers
respectively formed in both opposing surfaces of the first ion
conductive polymer layer; and a fourth ion conductive polymer layer
formed in one surface of each of the plurality of third ion
conductive polymer layers. That is, the polymer electrolyte
membrane includes a stack structure including `the fourth ion
conductive polymer layer/the third ion conductive polymer layer/the
first ion conductive polymer layer/the third ion conductive polymer
layer/the fourth ion conductive polymer layer`. In this connection,
a thickness of each of the third ion conductive polymer layer may
be in a range of 0.5% to 20% of the thickness of the polymer
electrolyte membrane, and a thickness of each of the fourth ion
conductive polymer layers may be in a range of 0.5% to 20% of the
thickness of the polymer electrolyte membrane. When this defined
range is met, the mechanical properties and chemical stability may
be secured at the same time while basically maintaining the ion
conductivity of the polymer electrolyte membrane, and the reaction
gas barrier ability of the polymer electrolyte membrane may be
particularly excellent. In this connection, in a specific example,
each of the thickness of each of the third ion conductive polymer
layer and the thickness of each of the fourth ion conductive
polymer layers may independently be 0.5% or more, 1.25% or more,
2.5% of or more, 3.75% or more, or 5% or more of the thickness of
the polymer electrolyte membrane and may independently be 20% or
less, 15% or less, 12.5% or less, or 10% or less of the thickness
of the polymer electrolyte membrane.
[0054] According to one embodiment of the present disclosure, the
thickness of the polymer electrolyte membrane may be in a range of
10 .mu.m to 100 .mu.m, 20 .mu.m to 80 .mu.m, or 40 .mu.m to 60
.mu.m. When this defined range is met, the polymer electrolyte
membrane may be suitable for use in the fuel cell, and the ion
conductivity, mechanical properties, and chemical stability thereof
may be secured. % as described above may be a percentage based on a
total thickness of the polymer electrolyte membrane.
[0055] According to one embodiment of the present disclosure, the
ion conductive polymer containing the sulfonic acid group may be a
sulfonated product of one or more polymers selected from a group
consisting of a fluoropolymer, a hydrocarbon-based polymer, and a
partially fluorinated polymer. In this case, the hydrogen ion
conduction ability and the reaction gas barrier ability may be
excellent.
[0056] According to one embodiment of the present disclosure, the
sulfonated fluoropolymer may be at least one selected from a group
consisting of a poly(perfluorosulfonic acid),
poly(perfluorocarboxylic acid) and a copolymer of fluorovinyl ether
and tetrafluoroethylene containing a sulfonic acid group.
[0057] According to one embodiment of the present disclosure, the
sulfonated hydrocarbon-based polymer may be at least one selected
from a group consisting of sulfonated polyimide, sulfonated
polyaryl ether sulfone, sulfonated polyetheretherketone, sulfonated
polybenzimidazole, sulfonated polysulfone, sulfonated polystyrene,
sulfonated polyphosphazenes, sulfonated polyetherethersulfones,
sulfonated polyethersulfones, sulfonated polyetherbenzimidazoles,
sulfonated polyarylene ether ketone, sulfonated polyether ketone,
sulfonated polystyrene, sulfonated polyimidazole, sulfonated
polyether ketone, and sulfonated polyaryl ether benzimidazole.
[0058] According to one embodiment of the present disclosure, the
sulfonated partially fluorinated polymer may be at least one
selected from a group consisting of sulfonated poly(arylene ether
sulfone-co-vinylidene fluoride), sulfonated
trifluorostyrene-grafted-poly(tetrafluoroethylene) and
styrene-grafted sulfonated polyvinylidene fluoride.
[0059] According to one embodiment of the present disclosure, the
first ion conductive polymer layer may include a porous substrate.
In a specific example, when the first ion conductive polymer layer
includes the porous substrate, the first ion conductive polymer
layer may be prepared from a first ion conductive polymer membrane
prepared by impregnating a porous reinforcing membrane with a
coated layer formation solution containing an ion conductive
polymer containing a sulfonic acid group, and drying and heating
the membrane. Thus, when the first ion conductive polymer layer
includes the porous substrate prepared from the porous reinforcing
membrane, this has an effect of further improving the mechanical
properties of the polymer electrolyte membrane.
[0060] According to one embodiment of the present disclosure, when
the first ion conductive polymer layer includes the porous
substrate, the first ion conductive polymer layer may include the
porous substrate; and a coated layer formed in each of both
opposing surfaces of the porous substrate, wherein the porous
substrate may have pores filled with the ion conductive polymer
containing a sulfonic acid group, wherein the coated layer may
include the ion conductive polymer containing a sulfonic acid
group. In a specific example, when the first ion conductive polymer
layer includes the porous substrate, the first ion conductive
polymer layer may include a stack structure of `the ion conductive
polymer layer including the sulfonic acid group/the porous
substrate having pores filled with the ion conductive polymer
containing the sulfonic acid group/the ion conductive polymer
containing the sulfonic acid group`.
[0061] According to one embodiment of the present disclosure, the
porous substrate may be prepared from the porous reinforcing
membrane, wherein the porous reinforcing membrane may be made of at
least one selected from a group consisting of
polytetrafluoroethylene, polyvinyldifluoroethylene, polyethylene,
and polypropylene. In another example, the porous reinforcing
membrane may be a stretched porous reinforcing membrane, wherein
the stretched porous reinforcing membrane may be made of at least
one selected from a group consisting of stretched
polytetrafluoroethylene, stretched polyvinyldifluoroethylene,
stretched polyethylene, and stretched polypropylene.
[0062] According to one embodiment of the present disclosure, the
polymer electrolyte membrane may have a hydrogen permeability
measured using a time-lag method which may be in a range of 18.5
Barrer or less, 1 Barrer to 18.5 Barrer, 10 Barrer to 18.5 Barrer,
14 Barrer to 18.5 Barrer, or 14.5 Barrer to 18.5 Barrer at
70.degree. C. When this defined range is met, the hydrogen gas
barrier ability may be excellent.
[0063] According to one embodiment of the present disclosure, the
polymer electrolyte membrane may have an oxygen permeability
measured using a time-lag method which may be in a range of less
than 4.0 Barrer, 1 Barrer to 3.9 Barrer, 2 Barrer to 3.8 Barrer, or
3 Barrer to 3.8 Barrer at 70.degree. C. When this defined range is
met, the oxygen gas barrier ability may be excellent.
[0064] Further, the present disclosure provides a polymer
electrolyte membrane preparation method for preparing the polymer
electrolyte membrane. The polymer electrolyte membrane preparation
method may include preparing a first ion conductive polymer
membrane including an ion conductive polymer containing a sulfonic
acid group (S10); performing a chlorination reaction in at least
one surface of the first ion conductive polymer membrane for 5 to
30 minutes such that a second ion conductive polymer membrane
including a chlorinated ion conductive polymer layer is formed in
at least one surface of a first ion conductive polymer layer,
wherein the chlorinated ion conductive polymer layer is formed by
partially chlorinating the sulfonic acid group (S20); performing a
nitrilation reaction in the second ion conductive polymer membrane
such that a third ion conductive polymer membrane including a
nitrilated ion conductive polymer layer is formed in at least one
surface of the first ion conductive polymer layer, wherein the
nitrilated ion conductive polymer layer is formed by replacing
chlorine in the chlorinated ion conductive polymer layer with a
nitrile group (S30); performing a hydrolysis reaction in the third
ion conductive polymer membrane such that a fourth ion conductive
polymer membrane including a second ion conductive polymer layer is
formed in at least one surface of the first ion conductive polymer
layer, wherein the second ion conductive polymer layer is formed by
replacing the nitrile group of the nitrilated ion conductive
polymer layer with a carboxylic acid group (S40); and performing
heat treatment of the fourth ion conductive polymer membrane at
.+-.10.degree. C. around a glass transition temperature of an ion
conductive polymer containing a carboxylic acid group, thereby
preparing the polymer electrolyte membrane (S50), wherein a
thickness of the second ion conductive polymer layer is in a range
of 1 to 80% of a thickness of the polymer electrolyte membrane.
[0065] According to one embodiment of the present disclosure, the
configurations of the polymer electrolyte membrane as described
above are equally applied to the polymer electrolyte membrane
preparation method unless otherwise specified.
[0066] According to one embodiment of the present disclosure, the
step (S10) includes preparing the first ion conductive polymer
membrane, wherein in preparing the polymer electrolyte membrane,
the first ion conductive polymer membrane may act as a base
membrane for forming the first ion conductive polymer layer prior
to forming the second ion conductive polymer layer in at least one
surface of the first ion conductive polymer layer, and for forming
the second ion conductive polymer layer in a subsequent step.
[0067] According to one embodiment of the present disclosure, the
first ion conductive polymer membrane may be an ion conductive
polymer membrane itself including a sulfonic acid group. In another
example, the first ion conductive polymer membrane may include the
porous substrate prepared by providing the porous reinforcing
membrane (S11); impregnating the porous reinforcing membrane with
the coated layer formation solution including an ion conductive
polymer (S12); and drying and/or heat-treating the porous
reinforcing membrane impregnated with the coated layer formation
solution (S13).
[0068] According to one embodiment of the present disclosure, the
step (S20) may include forming the second ion conductive polymer
membrane including the chlorinated ion conductive polymer layer
formed via partial chlorination of the sulfonic acid group in at
least one surface of the first ion conductive polymer layer,
wherein the step (S20) may be carried out via the chlorination
reaction for 5 to 30 minutes in at least one surface of the first
ion conductive polymer membrane.
[0069] According to one embodiment of the present disclosure, the
polymer electrolyte membrane prepared by the polymer electrolyte
membrane preparation method should have the mechanical properties
and chemical stability at the same time while maintaining the ionic
conductivity. Accordingly, the method for manufacturing the polymer
electrolyte membrane according to the present disclosure
essentially includes the heat treatment step (S50).
[0070] In this regard, as shown graphically in FIG. 1, it may be
identified from a dynamic mechanical analysis result based on the
type of the ion conductive group (sulfonic acid group and
carboxylic acid group) contained in the ion conductive polymer of
the polymer electrolyte membrane used in an embodiment of the
present disclosure, that the ion conductive polymer containing a
sulfonic acid group corresponding to the first ion conductive
polymer layer has a glass transition temperature (Ta) of
110.54.degree. C., while the ion conductive polymer containing a
carboxylic acid group corresponding to the second ion conductive
polymer layer has the glass transition temperature (Ta) of
98.25.degree. C.
[0071] That is, the first ion conductive polymer layer including
the ion conductive polymer containing a sulfonic acid group, and
the second ion conductive polymer layer including the ion
conductive polymer containing a carboxylic acid group as prepared
according to the polymer electrolyte membrane preparation method of
the present disclosure have different glass transition temperatures
as described above. Accordingly, when performing the heat treatment
step (S50) in preparing the polymer electrolyte membrane, change in
a morphology of each of the first ion conductive polymer layer and
the second ion conductive polymer layer occurs. Therefore, in order
to secure the reaction gas barrier ability as well as the
mechanical properties of the polymer electrolyte membrane, it is
necessary to maintain a packing density of the polymer electrolyte
membrane when preparing the polymer electrolyte membrane. In this
regard, according to the polymer electrolyte membrane preparation
method of the present disclosure, the packing density of the
polymer electrolyte membrane may be maintained by controlling the
thickness of the second ion conductive polymer layer as determined
via controlling of the reaction condition in the step (S20), and
controlling the heat treatment temperature in the step (S50) when
preparing the polymer electrolyte membrane.
[0072] According to one embodiment of the present disclosure, the
chlorination reaction of step (S20) may be carried out for 5
minutes to 30 minutes, 10 minutes to 30 minutes, or 20 minutes to
30 minutes. When this defined range is met, the thickness of the
second ion conductive polymer layer formed in at least one surface
of the first ion conductive polymer layer may be controlled.
[0073] According to one embodiment of the present disclosure, the
chlorination reaction of the step (S20) may be carried out by
immersing the first ion conductive polymer membrane in a
chlorination reaction solution containing hydrochloric acid and
ammonium chloride. In this connection, the chlorination reaction
solution may be a solution in which ammonium chloride is dissolved
in a concentrated aqueous hydrochloric acid solution. In a specific
example, the chlorination reaction solution may contain the
concentrated hydrochloric acid aqueous solution at 60 wt % to 90 wt
%, 70 wt % to 90 wt %, or 75 wt % to 85 wt % and the ammonium
chloride at 10 wt % to 40 wt %, 10 wt % to 30 wt %, or 15 wt % to
25 wt %. When this defined range is met, the thickness of the
second ion conductive polymer layer formed in at least one surface
of the first ion conductive polymer layer may be controlled.
[0074] According to one embodiment of the present disclosure, the
aqueous hydrochloric acid solution may have a concentration of
hydrochloric acid of 35 wt % or more, 35 wt % to 50 wt %, 35 wt %
to 40 wt %, or 35 wt % to 38 wt %, and may contain solid ammonium
chloride having a purity of 99.0 wt % or more, or 99.5 wt % or
more. The chlorination reaction solution may be a solution in which
the solid ammonium chloride is completely dissolved in the aqueous
hydrochloric acid solution.
[0075] According to one embodiment of the present disclosure, the
chlorination reaction of the step (S20) may be carried out at a
temperature of 60.degree. C. to 100.degree. C., 70.degree. C. to
90.degree. C., or 75.degree. C. to 85.degree. C. When this defined
range is met, the thickness of the second ion conductive polymer
layer formed in at least one surface of the first ion conductive
polymer layer may be controlled.
[0076] According to one embodiment of the present disclosure, the
chlorination reaction of the step (S20) may be carried out under an
inert gas atmosphere.
[0077] According to one embodiment of the present disclosure, the
step (S30) may include forming the third ion conductive polymer
membrane including the nitrilated ion conductive polymer layer in
at least one surface of the first ion conductive polymer layer,
wherein the nitrilated ion conductive polymer layer is formed by
replacing chlorine in the chlorinated ion conductive polymer layer
with a nitrile group. The step (S30) may be carried out via a
nitrilation reaction in the second ion conductive polymer
membrane.
[0078] According to one embodiment of the present disclosure, the
nitrilation reaction in the step (S30) is carried out to replace an
entirety of chlorine in the chlorinated ion conductive polymer
layer of the second ion conductive polymer membrane prepared in the
step (S20) with the nitrile group.
[0079] According to one embodiment of the present disclosure, the
nitrilation reaction of the step (S30) may be carried out by
immersing the second ion conductive polymer membrane in a
nitrilation reaction solution containing a nitrile salt. In this
connection, the nitrilation reaction solution may be a reaction
solution itself in which a nitrile salt is dissolved. In a specific
example, the nitrilation reaction solution may be a potassium
cyanide aqueous solution. In a more specific example, the potassium
cyanide aqueous solution may contain 0.01 M to 0.10 M, 0.03 M to
0.08 M, or 0.04 M to 0.06 M of potassium cyanide having a purity of
95.0 wt % or more, or 97.0 wt % or more.
[0080] According to one embodiment of the present disclosure, the
nitrilation reaction of the step (S30) may be carried out for 1
hour to 10 hours, 2 hours to 6 hours, or 3 hours to 5 hours.
[0081] According to one embodiment of the present disclosure, the
nitrilation reaction of the step (S30) may be carried out at a
temperature of 70.degree. C. to 110.degree. C., 80.degree. C. to
100.degree. C., or 85.degree. C. to 95.degree. C.
[0082] According to one embodiment of the present disclosure, the
nitrilation reaction of the step (S30) may be carried out under an
inert gas atmosphere.
[0083] According to one embodiment of the present disclosure, the
step (S40) may include forming the fourth ion conductive polymer
membrane including the second ion conductive polymer layer in at
least one surface of the first ion conductive polymer layer,
wherein the second ion conductive polymer layer is formed by
replacing the nitrile group of the nitrilated ion conductive
polymer layer with a carboxylic acid group. The step (S40) may be
carried out via the hydrolysis reaction in the third ion conductive
polymer membrane.
[0084] According to one embodiment of the present disclosure, the
hydrolysis reaction of the step (S40) may be carried out to replace
all of the nitrile groups of the nitrilated ion conductive polymer
layer of the third ion conductive polymer membrane as prepared in
the step (S30) with the carboxylic acid groups.
[0085] According to one embodiment of the present disclosure, the
hydrolysis reaction of the step (S40) may be carried out by
immersing the third ion conductive polymer membrane in boiling
water. In this connection, the boiling water may mean a state in
which water used for carrying out the hydrolysis reaction is
continuously heated at a temperature above the boiling point. In
this case, the water may be ion-exchanged water or distilled
water.
[0086] According to one embodiment of the present disclosure, the
hydrolysis reaction of the step (S40) may be carried out for 1 hour
to 10 hours, 1 hour to 5 hours, or 1 hour to 3 hours.
[0087] According to one embodiment of the present disclosure, the
hydrolysis reaction of the step (S40) may be carried out under an
atmospheric atmosphere.
[0088] According to one embodiment of the present disclosure, the
step (S50) may include preparing the polymer electrolyte membrane.
In the step (S50), the fourth ion conductive polymer membrane may
be heat-treated at .+-.10.degree. C. around a glass transition
temperature of the ion conductive polymer containing a carboxylic
acid group.
[0089] According to one embodiment of the present disclosure, in
order to maintain the packing density of the polymer electrolyte
membrane, as described above, it is necessary to control the heat
treatment temperature of the step (S50). Accordingly, the heat
treatment of the step (S50) may be performed at .+-.10.degree. C.,
.+-.5.degree. C., or .+-.3.degree. C. around the glass transition
temperature of the ion conductive polymer containing a carboxylic
acid group. In another example, the heat treatment of the step
(S50) may be carried out at 90.degree. C. to 105.degree. C.,
95.degree. C. to 105.degree. C., or 98.degree. C. to 102.degree. C.
In carrying out the heat treatment of the step (S50), when the heat
treatment is performed at an excessively high temperature without
considering the glass transition temperature of the ion conductive
polymer containing the carboxylic acid group as well as the glass
transition temperature of the ion conductive polymer containing the
sulfonic acid group, the heat treatment step may affect physical
properties of the ion conductive polymer containing the sulfonic
acid group such that the packing density of the polymer electrolyte
membrane is not maintained. When the heat treatment is performed at
a temperature too lower than the glass transition temperature of
the ion conductive polymer containing the carboxylic acid group,
the heat treatment step may not cause change in the physical
properties of the ion conductive polymer containing the carboxylic
acid group such that the packing density of the polymer electrolyte
membrane is not maintained.
[0090] According to one embodiment of the present disclosure, the
polymer electrolyte membrane preparation method may further include
drying the fourth ion conductive polymer membrane prepared in the
step (S40), prior to performing the heat treatment of the step
(S50). In this connection, the drying may be carried out for 12
hours to 36 hours, 18 hours to 30 hours, or 21 hours to 27
hours.
[0091] According to one embodiment of the present disclosure, in
the polymer electrolyte membrane preparation method, the step (S20)
may allow the thickness of the second ion conductive polymer layer
to be adjusted to be in a range of 1% to 80% of the thickness of
the polymer electrolyte membrane and at the same time, the step
(S50) may allow the packing density of the polymer electrolyte
membrane to be maintained.
[0092] Further, the present disclosure provides a
membrane-electrode assembly including the polymer electrolyte
membrane. The membrane-electrode assembly may include a
negative-electrode; a positive-electrode; and a polymer electrolyte
membrane interposed between the negative-electrode and the
positive-electrode, wherein the polymer electrolyte membrane may
include the polymer electrolyte membrane according to the present
disclosure.
[0093] According to one embodiment of the present disclosure, the
membrane-electrode assembly may be an assembly of an electrode in
which an electrochemical catalytic reaction between fuel such as
hydrogen gas and air containing oxygen occurs and a polymer
electrolyte membrane in which transfer of hydrogen ions occurs.
Alternatively, the membrane-electrode assembly may include the
negative-electrode, the positive-electrode and the polymer
electrolyte membrane interposed between the negative-electrode and
the positive-electrode which are adhered to each other.
[0094] According to one embodiment of the present disclosure, the
membrane-electrode assembly may further include a gas diffusion
layer disposed on one surface of each of the negative-electrode
(fuel electrode or hydrogen electrode) and the positive-electrode
(oxygen electrode or air electrode) for supplying the reaction gas.
In a specific example, the membrane-electrode assembly may be
interposed between the gas diffusion layer disposed on one surface
of the negative-electrode and the gas diffusion layer disposed on
one surface of the positive-electrode.
[0095] According to one embodiment of the present disclosure, the
membrane-electrode assembly may further include a catalyst layer
disposed on the other surface of each of the negative-electrode
(fuel electrode or hydrogen electrode) and the positive-electrode
(oxygen electrode or air electrode) for supplying the reaction gas.
In a specific example, the polymer electrolyte membrane may be
interposed between the catalyst layer disposed on the other surface
of the negative-electrode and the catalyst layer disposed on the
other surface of the positive-electrode.
[0096] According to one embodiment of the present disclosure, the
membrane-electrode assembly may have at least one stack structure
selected from a group consisting of negative-electrode/polymer
electrolyte membrane/positive-electrode, gas diffusion
layer/negative-electrode/polymer electrolyte
membrane/positive-electrode, negative-electrode/polymer electrolyte
membrane/positive-electrode/gas diffusion layer, gas diffusion
layer/negative-electrode/polymer electrolyte
membrane/positive-electrode/gas diffusion layer,
negative-electrode/catalyst layer/polymer electrolyte
membrane/positive-electrode, negative-electrode/polymer electrolyte
membrane/catalyst layer/positive-electrode,
negative-electrode/catalyst layer/polymer electrolyte
membrane/catalyst layer/positive-electrode, gas diffusion
layer/catalyst layer/negative-electrode/polymer electrolyte
membrane/positive-electrode, gas diffusion
layer/negative-electrode/polymer electrolyte membrane/catalyst
layer/positive-electrode, gas diffusion layer/catalyst
layer/negative-electrode/polymer electrolyte membrane/catalyst
layer/positive-electrode, negative-electrode/polymer electrolyte
membrane/catalyst layer/positive-electrode/gas diffusion layer,
negative-electrode/catalyst layer/polymer electrolyte
membrane/positive-electrode/gas diffusion layer,
negative-electrode/catalyst layer/polymer electrolyte
membrane/catalyst layer/positive-electrode/gas diffusion layer, and
gas diffusion layer/catalyst layer/negative-electrode/polymer
electrolyte membrane/catalyst layer/positive-electrode/gas
diffusion layer.
[0097] According to one embodiment of the present disclosure, the
catalyst layer of each of the negative-electrode and the
positive-electrode may include a catalytic metal and a conductive
material on which the catalytic metal is supported. The catalyst
may include a metal that promotes an oxidation reaction of hydrogen
and a reduction reaction of oxygen. Specific examples thereof may
include platinum, gold, silver, palladium, iridium, rhodium,
ruthenium, iron, cobalt, nickel, chromium, tungsten, manganese,
vanadium, and alloys thereof. Further, the conductive material may
be activated carbon. Further, the catalyst layer of each of the
negative-electrode and the positive-electrode may include an ion
conductive polymer identical with the ion conductive polymer as an
electrode binder.
[0098] According to one embodiment of the present disclosure, the
membrane-electrode assembly may be prepared via compression such as
thermocompression bonding of the negative-electrode; the
positive-electrode; and the polymer electrolyte membrane interposed
between the negative-electrode and the positive-electrode which are
in close contact with each other. Further, the membrane-electrode
assembly may be prepared by directly applying and drying a catalyst
layer slurry for forming the catalyst layer of each of the
negative-electrode and the positive-electrode on one surface or
both opposing surfaces of the polymer electrolyte membrane.
[0099] According to one embodiment of the present disclosure, the
gas diffusion layer may have a double-layer structure composed of a
micro-porous layer (MPL) and a macro-porous substrate. The
microporous layer may be prepared by mixing carbon powders such as
acetylene black carbon, or black pearls carbon with a
polytetrafluoroethylene (PTFE)-based hydrophobic agent. Then, the
MPL may be applied on one surface or both opposing surfaces of the
macro-porous substrate depending on applications. The macro-porous
substrate may be composed of carbon fibers and
polytetrafluoroethylene-based hydrophobic material. In a specific
example, the carbon fibers may employ carbon fiber clothes, carbon
fiber felts, and carbon fiber papers.
[0100] Further, the present disclosure provides a fuel cell
including the membrane-electrode assembly. The fuel cell may
include a stack, a fuel supply, and an oxidizing agent supply.
[0101] According to one embodiment of the present disclosure, the
stack may include at least one membrane-electrode assembly. When
the stack has two or more membrane-electrode assemblies, the stack
may further include a bipolar plate interposed therebetween. The
bipolar plate serves as a conductor connecting the
negative-electrode and the positive-electrode in series with each
other while delivering the fuel and the oxidizing agent supplied
from an outside to the membrane-electrode assembly.
[0102] According to one embodiment of the present disclosure, the
fuel supply may be intended to supply the fuel to the stack. The
fuel supply may include a fuel tank for storing the fuel and a pump
for supplying the fuel stored in the fuel tank to the stack. The
fuel may be gas or liquid state hydrogen or hydrocarbon fuel.
Examples of the hydrocarbon fuel may be alcohols such as methanol,
ethanol, propanol and butanol, or natural gas.
[0103] According to one embodiment of the present disclosure, the
oxidizing agent supply may supply the oxidizing agent to the stack.
The oxidizing agent may be typically the air. The oxygen or air may
be injected using a pump.
[0104] According to one embodiment of the present disclosure, the
fuel cell may include a polymer electrolyte membrane fuel cell, a
direct liquid fuel cell, a direct methanol fuel cell, a direct
formic acid fuel cell, a direct ethanol fuel cell, or a direct
dimethyl ether fuel cell.
[0105] Hereinafter, Examples of the present disclosure will be
described in detail so that a person having ordinary knowledge in
the technical field to which the present disclosure belongs may
easily implement the disclosure. However, the present disclosure
may be implemented in several different forms and is not limited to
Examples described herein.
EXAMPLES
Example 1
[0106] <Preparation of First Ion Conductive Polymer
Membrane>
[0107] Nafion 212 as a poly(perfluorosulfonic acid)polymer membrane
having a thickness of 50.8 .mu.m was prepared as the first ion
conductive polymer membrane.
[0108] <Chlorination Reaction>
[0109] 20 parts by weight of ammonium chloride having a purity of
99.5wt % (Sigma Aldrich) was added to 80 parts by weight of aqueous
hydrochloric acid solution (Sigma Aldrich) having a concentration
of 37 wt %. We completely dissolved the ammonium chloride at
80.degree. C. to prepare a chlorination reaction solution.
[0110] The first ion conductive polymer membrane was immersed in
the chlorination reaction solution. The chlorination reaction was
performed while refluxing at 80.degree. C. for 5 minutes under
nitrogen atmosphere, thereby preparing the second ion conductive
polymer membrane.
[0111] <Nitrilation Reaction>
[0112] Potassium cyanide (Sigma Aldrich) having a purity of 97.0 wt
% was used to prepare 0.05 M potassium cyanide aqueous solution at
90.degree. C. Thus, a nitrilation reaction solution was
prepared.
[0113] The second ion conductive polymer membrane was immersed in
the nitrilation reaction solution, and the nitrilation reaction was
performed while refluxing at 90.degree. C. for 4 hours under
nitrogen atmosphere. Thus, the third ion conductive polymer
membrane was prepared.
[0114] <Hydrolysis Reaction>
[0115] Ion-exchanged water was boiled at a temperature of
100.degree. C. to prepare a hydrolysis reaction solution.
[0116] The third ion conductive polymer membrane was immersed in
the hydrolysis reaction solution, and a hydrolysis reaction was
performed in the boiling water for 2 hours under an atmospheric
atmosphere. Thus, the fourth ion conductive polymer membrane was
prepared.
[0117] <Drying and Heat Treatment>
[0118] After drying the fourth ion conductive polymer membrane at
room temperature for 24 hours, heat treatment was performed at
atmospheric pressure and 100.degree. C. for 1 hour, thereby
preparing a polymer electrolyte membrane.
Example 2
[0119] A polymer electrolyte membrane was prepared in the same
manner as in Example 1, except that during the chlorination
reaction, the first ion conductive polymer membrane was immersed in
the chlorination reaction solution, and the chlorination reaction
was performed while refluxing at 80.degree. C. and for 30 minutes
under a nitrogen atmosphere, thereby preparing the second ion
conductive polymer membrane.
Comparative Example 1
[0120] Nafion 212 as a polymer membrane made of
poly(perfluorosulfonic acid) and having a thickness of 50.8 .mu.m
was used as the polymer electrolyte membrane.
Comparative Example 2
[0121] <Preparation of Ion Conductive Polymer Membrane>
[0122] Nafion 212 as a poly(perfluorosulfonic acid) polymer
membrane having a thickness of 50.8 .mu.m was prepared as an ion
conductive polymer membrane.
[0123] <Drying and Heat Treatment>
[0124] The ion conductive polymer membrane was heat-treated under
atmospheric pressure and 100.degree. C. and for 1 hour, thereby
preparing a polymer electrolyte membrane.
Comparative Example 3
[0125] A polymer electrolyte membrane was prepared in the same
manner as in Example 1, except that during the chlorination
reaction, the first ion conductive polymer membrane was immersed in
the chlorination reaction solution, and the chlorination reaction
was performed while refluxing at 80.degree. C. and for 30 secs
under a nitrogen atmosphere, thereby preparing the second ion
conductive polymer membrane.
Comparative Example 4
[0126] A polymer electrolyte membrane was prepared in the same
manner as in Example 1, except that during the chlorination
reaction, the first ion conductive polymer membrane was immersed in
the chlorination reaction solution, and the chlorination reaction
was performed while refluxing at 80.degree. C. and for 40 minutes
under a nitrogen atmosphere, thereby preparing the second ion
conductive polymer membrane.
Experimental Examples
Experimental Example 1
[0127] In the polymer electrolyte membrane prepared in Example 2,
hydrogen ions were replaced with sodium ions. Thus, a cross section
of the polymer electrolyte membrane was imaged and analyzed via a
line scan method using SEM-EDX (Scanning Electron Microscope-Energy
Dispersive X-ray Spectrometer). Results are shown in FIG. 2.
[0128] As shown in FIG. 2, it was identified that the polymer
electrolyte membrane of Example 2 prepared according to the present
disclosure had the first ion conductive polymer layer including the
ion conductive polymer containing a sulfonic acid group, and the
second ion conductive polymer layer including the ion conductive
polymer containing a carboxylic acid group and formed in each of
both opposing surfaces of the first ion conductive polymer layer.
It was identified that a total thickness of the second ion
conductive polymer layer was about 40% of a thickness of the
polymer electrolyte membrane.
Experimental Example 2
[0129] A total thickness of the second ion conductive polymer layer
of each of the polymer electrolyte membranes prepared in Example 1
and Comparative Examples 1 to 4 was identified in the same manner
as in Experimental Example 1, and is shown in Table 1 below.
[0130] Further, a thickness of the second ion conductive polymer
layer, hydrogen permeability, oxygen permeability, and ionic
conductivity, of each of the polymer electrolyte membranes prepared
in Examples 1 and 2 and Comparative Examples 1 to 4 were measured
using a following method and are described together in Table 1
below. A ratio of the thickness of the second ion conductive
polymer layer to the thickness of the polymer electrolyte membrane
is converted into a percentage and is described in Table 1
below.
[0131] Further, the measurement results of the hydrogen
permeability and the oxygen permeability based on a temperature of
each of the polymer electrolyte membranes as prepared in Examples 1
and 2 and Comparative Examples 1 and 2 are shown in graphs of FIG.
3 and FIG. 4, respectively.
[0132] the thickness (um) was measured using VL-50 from MITUTOYO
(Japan).
[0133] Hydrogen permeability (Barrer): The hydrogen permeability of
each of the polymer electrolyte membranes as prepared in Examples 1
and 2 and Comparative Examples 1 to 4 was measured using the
time-lag method. The hydrogen permeability at 70.degree. C. is
shown. Specifically, a time-lag hydrogen permeability measurement
apparatus had two chambers separated from each other via the
polymer electrolyte membrane prepared in each of Examples 1 and 2
and Comparative Examples 1 to 4 and having different pressures.
While one chamber was maintained at a pressure of 0 atm, hydrogen
gas was introduced into the other chamber so that a pressure
therein was changed to 1 atm. Then the hydrogen gas permeated into
the polymer electrolyte membrane at a temperature of 30 to
70.degree. C. and for 2 hours or less. Then, a value obtained by
multiplying a permeation flow rate into the polymer electrolyte
membrane per an unit area, a unit time and a pressure by the
membrane thickness was converted into a Barrer unit (1
Barrer=10.sup.-10 (cm*cm.sup.3)/(cm.sup.2*s*cm Hg)).
[0134] Oxygen permeability (Barrer): The oxygen permeability of
each of the polymer electrolyte membranes as prepared in Examples 1
and 2 and Comparative Examples 1 to 4 was measured using the
time-lag method. The oxygen permeability at 70.degree. C. is shown.
Specifically, a time-lag oxygen permeability measurement apparatus
had two chambers separated from each other via the polymer
electrolyte membrane prepared in each of Examples 1 and 2 and
Comparative Examples 1 to 4 and having different pressures. While
one chamber was maintained at a pressure of 0 atm, oxygen gas was
introduced into the other chamber so that a pressure therein was
changed to 1 atm. Then the oxygen gas permeated into the polymer
electrolyte membrane at a temperature of 30 to 70.degree. C. and
for 2 hours or less. Then, a value obtained by multiplying a
permeation flow rate into the polymer electrolyte membrane per an
unit area, a unit time and a pressure by the membrane thickness was
converted into a Barrer unit (1 Barrer=10.sup.-10
(cm*cm.sup.3)/(cm.sup.2*s*cm Hg)).
[0135] Ionic conductivity (S/cm): Na.sup.+ ion conductivity in each
of the polymer electrolyte membranes prepared in Examples 1 and 2
and Comparative Examples 1 to 4 was measured at a temperature of
80.degree. C. and a relative humidity of 50%. Specifically, ohmic
resistance or bulk resistance was measured using a four point probe
AC impedance spectroscopic method. Then, the Na.sup.+ ion
conductivity was calculated using Equation 1 below.
.sigma.=L/RS [Equation 1]
[0136] .sigma. denotes the Na+ ion conductivity (S/cm), R denotes
the ohmic resistance (.OMEGA.) of the polymer electrolyte membrane,
L denotes a distance (cm) between electrodes, and S denotes an area
(cm.sup.2) of the electrolyte in which a constant current
flows.
TABLE-US-00001 TABLE 1 Example Comparative Example Examples 1 2 1 2
3 4 Total thickness of (.mu.m) 10.0 20.0 -- -- -- 50.0 second ion
conductive polymer layer Thickness of polymer (.mu.m) 50.0 50.0
50.8 50.0 50.3 50.2 electrolyte membrane Ratio of thickness of (%)
20.0 40.0 0 0 0 99.6 second ion conductive polymer layer Hydrogen
permeability (Barrer) 18.30 14.64 19.90 18.90 19.50 12.90 Oxygen
permeability (Barrer) 3.77 3.11 4.07 4.00 4.02 2.10 Ionic
conductivity (S/cm) 0.029 0.024 0.028 0.031 0.025 0.011
[0137] As shown in Table 1, FIG. 3 and FIG. 4, it could be
identified that the polymer electrolyte membrane prepared according
to the present disclosure had the same thickness and exhibited the
same ionic conductivity, and lowered hydrogen permeability and
oxygen permeability because the second ion conductive polymer layer
was formed at an appropriate thickness ratio, compared to
Comparative Example 1 free of any treatment on the ion conductive
polymer membrane and Comparative Example 2 where only the heat
treatment step was performed. In particular, it was identified that
in Example 2, hydrogen permeability and oxygen permeability were
significantly reduced, and thus the reaction gas barrier ability
was very excellent.
[0138] On the contrary, in Comparative Example 3 in which a series
of steps including the chlorination reaction were performed on the
polymer electrolyte membrane, and the chlorination reaction
duration was very short, the second ion conductive polymer layer to
be formed in accordance with the present disclosure was not formed
at all. Accordingly, each of hydrogen permeability and oxygen
permeability as well as ionic conductivity thereof was maintained
at a level similar to that of each of Comparative Examples 1 and 2
and thus was not improved.
[0139] Further, in Comparative Example 4 in which a series of steps
including the chlorination reaction were performed on the polymer
electrolyte membrane, and the chlorination reaction duration was
larger than that in Example 2, the second ion conductive polymer
layer constituted a substantial amount of the polymer electrolyte
membrane. Thus, sharp decrease in a proportion of the first ion
conductive polymer layer occurred. Thus, the ionic conductivity was
very poor.
[0140] It could be identified from these results that the polymer
electrolyte membrane according to the present disclosure has high
hydrogen ion conductivity and excellent reaction gas barrier
ability.
[0141] The polymer electrolyte membrane according to the present
disclosure has a high hydrogen ion conductivity and an excellent
reaction gas barrier ability.
[0142] Further, the membrane-electrode assembly including the
polymer electrolyte membrane according to the present disclosure
has an excellent reaction gas barrier ability.
[0143] Further, in the fuel cell including the membrane-electrode
assembly according to the present disclosure, the thinning and the
pinhole resulting from structural decomposition of the polymer
electrolyte membrane due to the reaction gas permeation may be
prevented. Thus, the fuel cell has a long lifespan.
[0144] Hereinabove, although the present disclosure has been
described with reference to exemplary embodiments and the
accompanying drawings, the present disclosure is not limited
thereto, but may be variously modified and altered by those skilled
in the art to which the present disclosure pertains without
departing from the spirit and scope of the present disclosure
claimed in the following claims.
* * * * *